The Endophthalmitis Vitrectomy Study (EVS) is a prospective, randomized, multicenter clinical trial with the primary goal of determining the role of pars plana vitrectomy in the initial management of patients with bacterial endophthalmitis following cataract surgery or secondary lens implantation. Patients who meet entry criteria will be treated with one of two presently accepted strategies for the management f bacterial endophthalmitis. Eyes will be randomized to either 1) initial pars plana vitrectomy with intravitreal antibiotics, followed by retap and reinjection at 36-60 hours for eyes doing poorly as defined in the study, or 2) initial anterior chamber and vitreous tap/biopsy with injection of intravitreal antibiotics, followed by vitrectomy and reinjection at 36-60 hours in eyes doing poorly. In addition, all eyes will be randomized to the use or non use of intravenous antibiotics. Study endpoints are visual acuity and clarity of ocular media, the latter assessed both clinically and photographically. Initial endpoint assessment will occur at 3 months, after which late procedures which may be required to improve vision, such as late vitrectomy to clear non-clearing ocular media, may be performed. Final outcome assessment will occur at 9 months. Multiple centers will cooperate in enrolling 420 eyes during a recruitment period of 42 months. This is the lead application, being submitted in conjunction with an application for a coordinating center, and for a photo reading center. Applications for clinical centers will be solicited once the study design is approved. A draft manual of operations for the study is included as an integral part of this application.